Feature request: fail quickly without a prompt when run non-interactively

[jayconrod]

I'm using go-keyring in a small credential helper for a build tool. The build tool invokes the credential helper to obtain headers to send to a remote service. Communication is over pipes bound to stdin, stdout, so even when the build tool is invoked interactively, the credential helper doesn't have access to the terminal, and the user can't enter a password.

It looks like keyring.Get may display a prompt, waiting for user input in some cases. This happens in secret_service.SecretService.handlePrompt. When this path is reached, the build tool hangs, then times out and kills the credential helper.

I'd like some way to avoid displaying a prompt or doing something that might require using input. I'd be happy for keyring.Get to return a distinctive error, so my credential helper can display an actionable message to the user.